The study of regulation of rat insulin promoter I by lipid synthetic transcription factors, SREBPs
| Project/Area Number |
15590284
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Pathological medical chemistry
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| Research Institution | Okinaka Memorial Institute for Medical Research. |
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Principal Investigator |
AMEMIYA Michiyo Okinaka Memorial Institute for Medical Research, Reseache, 研究員 (00288101)
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| Co-Investigator(Kenkyū-buntansha) |
MURASE Toshio Okinaka Memorial Institute for Medical Research, Director, 所長 (60107612)
SHIMANO Hitoshi University of Tsukuba, Institute of Clinical Medicine, Department of Internal Median, Assistant Professor, 大学院・人間総合科学研究科・内分泌代謝・糖尿病内科, 講師 (20251241)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2003: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Keywords | Diabetes Mellitus / SREBP / Insulin / Transcription / Lipotoxicity / Lipid metabolis |
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| Research Abstract |
A possible role of de novo lipid synthesis in the lipotoxicity for pancreatic β-cells has not been fully understood. As an initial step to study this issue, potential effects of sterol regulatory element binding proteins (SREBPs), lipid synthetic transcription factors, on insulin gene expression were investigated.
Promoter analysis for a rat insulin I promoter was performed using transfection studies in non-β-cells (HepG2) with a luciferase reporter gene system. Expression plasmids encoding nuclear human SREBP isoforms (SREBP-1a, -1c or -2) and rat β-cell-specific factors(PDX1, BETA2 and E47) were co-transfected.
In luciferase assays, any of SREBP isoforms markedly up-regulated the activity of the insulin promoter (-715 bps containing all known functional cis-elements) to the extent equal to that by co-expression of PDX1/BETA2/E47. In the sequence of the rat insulin I promoter, three potential SRE sites (SRE1, SRE2 and SRE3) were newly identified. The SRE1 and SRE2 were located adjacent to E1 and E2 boxes, respectively. Sequential deletion studies supported these three SREs all contributed to the activation. Binding of SREBP proteins to these elements were confirmed by EMSA analysis. Intriguingly, the SREBP-1c activation of the insulin promoter was further enhanced by the presence of BETA2/E47, but not PDX1. Through the extensive mutation analysis for different SRE and E box domains, it was found that especially both E1 and E2 boxes are crucial for the synergistic effects of SREBP/BETA2/E47. In similar studies for rat insulin II promoter, activation by SREBP-1c alone was also observed, but not SREBP-1c/BETA2/E47 as well as PDX1/BETA2/E47 synergism.
Our results demonstrate that SREBPs have potent transcriptional activities for insulin gene promoters in non-β cells. Although these novel effects of SREBPs need to be estimated in β-cells, the transactivity of SREBP-1c for insulin gene could be involved in the complex pathophysiology of β-cell specific lipotoxicity.
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Report
(3 results)
Research Products
(10 results)
